Immunity
by lesyeuxverts
Summary: The sequel to Vaccinations: Snape attempts to learn more about Harry's mysterious immune system but fails. Harry attempts to practice Occlumency and with Hermione's help, succeeds.


I make no claim to any of the characters, settings, ideas, etc. that belong to J.K. Rowling.

This is the sequel to "Vaccinations" and will probably make more sense if you've read that first. I currently have plans for another one-shot that will follow this and complete the story, but I don't know when I'll finish it. Please read and review, it makes me so very happy.

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Severus Snape, with a sneer curling his lip, kept that irritating chit Granger after class. She stood fidgeting in front of his desk, typical Gryffindor arrogance temporarily squashed. Snape ignored her, scrutinized the potion samples that had been turned in at the end of class. He allowed the vial that contained Granger's potion – gleaming fragile glass filled with the sparkling red blood replenishing potion – to slip from his slender bony fingers and thud hard against the wooden desk. The nosy bookworm had charmed it unbreakable – what a pity, that. He'd have liked to dock her grade while she watched the fruit of her study and labor ooze out onto his desk, sticky red in the sharp shards of the broken vial.

Granger's potion was perfect, of course, with that daft Weasley no longer in his class to distract her and with the irritating empty-headed Potter still in the infirmary after the fiasco that had been made of his vaccinations. Snape, after a lengthy session with the Cruciatus curse and administration of a truth serum more potent than Veritaserum, might have admitted that the younger Potter was both more tolerable than the elder Potter and more skilled at Potions. Fortunately, he was not required to admit that both Granger and Potter were competent and produced perfect potions in front of either the smug, infuriating Headmaster or his slimy, sneaky Slytherins.

At length, Snape looked up at Granger, found her biting her lip and twisting those unmanageable curls in her hand. A pale complexion framed wide dark eyes. A Slytherin knew that in humans, as in nature, there were predators and prey and a successful Slytherin chose which role to take. Snape smirked at the dark doe-like eyes, the pale face, certain that this intimidated Gryffindor would be easy prey.

"You wanted to speak with me, sir?" she asked when she had his attention.

A nod made the curtain of greasy hair that framed his face sway. "Sit," he ordered her. "I wish to know more about the situation that was discussed in the infirmary. Specifically, I want to see the Arithmancy that you have done and know any evidence that supports your conclusion. Pomfrey will also want more information detailing these hypothesized changes to Potter's immune system."

Granger dropped into the chair nearest his desk like a leaf dropping into a river, unstable and jerky and looking as though she'd rather be anywhere else. Snape was convinced by her uncertain movements, despite her words, that she was the prey to his predator. He leaned forward to intimidate her, kept his gaze fixed on her, waited for the prey to fall into his trap.

"I really can't betray Harry's confidence in me any more than I already have done, Professor," she said.

With a smirk at the futile struggle of the prey, the predator chose the bait for the trap. Snape selected a book from one of the piles on his desk and held it out, balanced on one large palm. "This, Miss Granger, is the best and most definitive resource on Occlumency. Unfortunately for you, it's out of print and unavailable in the library and most wizarding bookstores because there simply isn't enough demand for it. I might be persuaded to loan my personal copy to you in order to further Mr. Potter's studies if I had sufficient … incentive … to do so."

Snape leaned back, intimidation tactics set aside while the prey considered the bait. The Slytherin inside triumphed but Snape kept his face impassive. He waited as though uninterested by Granger's response, not that he expected the bookworm to do anything other than accept the bribe.

"That's despicable," Granger spat. Snape was reminded of the unfortunate consequences that arose from using Slytherin machinations on a Gryffindor. The jerking, stumbling, uncertain feeling inside his chest that was the sense of the prey escaping the trap was a feeling that Snape had always hated. "You've had that book all this time and you've been letting Harry struggle. I bet you've been laughing at him behind his back, knowing that you had the tools to ensure he succeeded and were deliberately withholding them. You've always been like that with Harry, even in first year Potions when you charmed the chalkboard so that there was always one important line he couldn't see." She paused for breath, pushing her hair back from her flushed face. Her eyes gleamed, reminding Snape of the shine of firelight off of potions vials filled with pure Veritaserum, clear and sparkling and smooth.

He had been wrong. This Gryffindor girl, annoying bookworm and meek student and interfering know-it-all, she was not easy prey. His trap had been too obvious, his bait had been wrong. The muscles around Snape's eyes twitched as he began to plan a retreat.

"You thought we wouldn't notice because you think Gryffindor is a synonym for stupid, Professor. You and your favorite little Slytherins can look down on me because I'm a Gryffindor or because I'm not an inbred pureblood that can barely tie a pair of shoelaces without help. But in the end, what matters aren't the names you call me, but the facts that I have. I've got proof of your vicious, vindictive behavior towards Harry. I found the charm on the chalkboard, I've got evidence of every mistake you helped Harry make in Potions, and I have records of every insult you've given him in class, every unfair grade and every undeserved detention. Now I have this, the proof that you've been hindering our efforts against You-Know-Who, proof that you aren't helping Harry learn Occlumency to the best of your ability as you should be."

The girl laid her hands on Snape's desk, sweaty palms that left a mark on the heavy wood, and leaned toward Snape. "You've just given me the most damning piece of evidence of all," she said, "and I'm quite prepared to speak with the Headmaster about it."

Snape's lips had fallen slack out of their habitual sneer. His black eyes gave no hints of his emotions as he stared at Granger without flinching. Using Slytherin tactics on a Gryffindor was indeed a bad idea, particularly when the Gryffindor was as perceptive and strong-minded as this one, particularly when the Gryffindor was not prey to the Slytherin predator. With any one of his Slytherins, Snape would have had a hundred graceful exits out of this situation, a hundred evasions or half-truths or counters, because Slytherins understood the dance of predator and prey. With this Gryffindor chit, who was bloody-minded and steel-hearted and set against him – he could see it in the flash of light in her eyes – he had no choice. Snape set the book on the desk and pushed it toward Granger with the rough sound of leather scraping against wood until it came to rest between her hands. "Very Slytherin of you, Miss Granger. I concede the point, but you are to return this to me in good condition once you've finished with it, do you understand?"

The irritating girl gave a curt nod and cradled the book in gentle hands. She rose to leave, but Snape stopped her with a harshly said, "Ten points to Gryffindor for the use of positively Slytherin methods." The word blackmail hung in the air between them, poised and unspoken.

She turned then, without a Gryffindor protest at being awarded House points for blackmail. She turned and faced him, met his gaze with her eyes glinting – the shine in them still reminded Snape of glass, smooth and brittle and yet somehow unbreakable – and said, "You will no longer do anything to the detriment of Harry's Potions grade, either in class or out of it, Professor, and you will not pry into his confidential medical records either." With those final words having slipped off her tongue to vibrate, low and soft in the dungeon air, she turned and left.

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Next Monday week, Potter and Granger appeared for the Occlumency lesson as scheduled, in Snape's office full of disgusting things in glass jars. Snape watched Granger evaluate the room, could practically hear her drooling over the rare books and cataloging the specimens – full-grown Mandrake root in formaldehyde, intestine of an eel harvested during the new moon, adder's tongues preserved in saline solution – without the use of Legilimency. Her thoughts were visible on her face, reckless bookish Gryffindor that she was, uninterested in subtlety and disguise.

"Sit," he said. Two of the chairs had been cleared of their piles – abysmal essays written by pathetic excuses for students, Potions tomes, dust – and Potter and Granger sat in them.

Potter had been released from the infirmary on Friday and still looked shaky, with rings under his eyes and his hair more of a disaster than usual. Potter's hair was the only thing at Hogwarts less tamable than Potter himself, as Snape often told Dumbledore – to which the response was always the offer of tea and a cryptic comment that enlightened no one other than the Headmaster.

Snape studied the boy – all pale translucence and angles like a Renaissance oil painting of a martyr, just as he usually looked – and wondered about the state of his health. Pomfrey thought that the shock of the vaccination experience had permanently weakened his heart – "So long as it didn't weaken his brain, Poppy, he's got nothing to spare in that department" – and the boy looked it, looked now more like he was a portrait of himself, kept under glass and allowed to fade in the sun.

"I trust that you've taken advantage of the break in our regular schedule to practice," Snape sneered at Potter, "and that Miss Granger has had ample time to prepare both herself and yourself for this lesson?"

With a short pause, Snape allowed the boy to prepare for the attack. The Headmaster would see, if that irritating Gryffindor girl ever complained, if he had access to Snape's side of the story, that he was being more than fair to a whining arrogant brat who deserved far less consideration. "Legilimens," Snape whispered.

His mental probe – confident and unaccustomed to resistance from this tempting target of a boy – slammed into the wall of Potter's Occlumency. A gasp, a gulp of cold dungeon air into his lungs brought some balance of reality to Snape as he was overwhelmed by pain. It was a hazy red vortex that sucked him in to the center of pain – pain, sharp and harsh and unrelenting – and Severus struggled to orient himself.

In his office, Snape saw with eyes that could barely focus, Granger had dropped to the floor next to Potter's chair. The girl took Potter's wrist in his hand and was speaking in low tones. "Harry, you can do this, you know you can do this, just as we practiced. Breathe in and out, take deep breaths, breathe every time I tap my fingers on your wrist, okay? Breathe for me, Harry, you can do it."

Potter had chosen a memory for his defense, Snape noted while he struggled to keep his mind above that vortex of pain. It was alarming to think that a boy of Potter's age had suffered this much pain, but then again, James Potter's son was practically asking for pain with all of his arrogant death-defying stunts. Snape sharpened his mind and pushed – directionless, searching for a way to get through this memory.

He heard a whisper that brushed against his nerves, a brief blessed respite from pain. "… Frightened by a small little needle …" a voice said somewhere off to his left and Snape moved toward it.

Rows and rows of sharp silver needles, they gleamed in the sunlight next to rows and rows of glass potion vials filled with serums – pink and sludge green and clear and blue. The sunlight came from an open window. Snape sent his mental probe moving toward it and was wrenched away, back into the memory.

A branching vine-like network enveloped him and the world was red and pain and swirled around him. Somewhere Snape, with his real arm reached out to grasp a real desk – firm wood under his palm – to steady himself against the whirlpool. The vines looped around his mind tightened and twisted and pulled at him while the pain increased, soaring to a fever pitch like a banshee with operatic aspirations.

Snape wrenched himself out of Potter's defenses, ripping his mind away and sending it through the mental ether to the beckoning lodestone that was his body. Dungeon air filled his lungs – damp and cold and calming – and Snape forced his fingers to unclench from the edge of the desk.

"That was an interesting and rather unorthodox choice of defense. The infirmary and your aborted vaccinations, I assume," Snape said. Potter met his gaze and for the first time this year didn't hesitate to do so, didn't hesitate to be open for a potential mental attack. The boy nodded. His green eyes were clear and guarded. There were fine lines etched into the young skin of his face – clustered around his eyes and forehead. In one heartbeat, Snape saw a boy sitting before him, a boy who was neither Slytherin nor Gryffindor but only a boy who was tired, shaky and ill, a boy who had suffered. That a boy so young should have suffered so much pain at Snape's own hands …

Snape extracted a vial of a thick purple potion from his desk drawer and held it in fingers that he did not allow to tremble. "Dreamless Sleep potion, Potter, is not a substitute for Occlumency. You will clear your mind before you sleep every night as this potion is doubtless ineffective against visions sent by the Dark Lord. Do not expect any leniency from your professors if you overdose on this potion and remain groggy in class. As we've covered Dreamless Sleep potion in class, I'll trust that either you remember the normal dosage and warnings about its use or that Miss Granger can remind you."

He passed the vial to the boy – allowed his fingers to brush against the boy's fingers in order for the boy to feel that Snape's fingers did not tremble. Then, with a sharp jerk of his head and wave of his hand – it did not tremble – he dismissed the two annoying Gryffindors.


End file.
